The present paper reports a comprehensive first-principles calculation of the structural, electronic and thermophysical properties of B1, B2 and B3 phases of AlSi (Silumine) alloy using plane-wave pseudopotential density functional theory (DFT). PAW type pseudopotential with the exchange correlation of Perdew-Burke-Ernzerhof (PBE) are used to compute properties of B1, B2 and B3 phases of AlSi alloy. Our computed equilibrium lattice constants are in excellent agreement with the reported results. To investigate the structural phase transitions beween different phases of AlSi alloy, volume dependence of energy and pressure dependence of enthaply are studied for B1, B2 and B3 phases of AlSi alloy. Further, the electronic band structure along with the total electronic density of states of B1, B2 and B3 phases of AlSi alloy are calculated at the ground states. Behaviour of the total electronic density of states of B1, B2 and B3 phases of AlSi is also studied with the increase in pressure up to 100 GPa. In addition, various finite temperature/pressure thermophysical properties such as the room temperature thermal equation of state, isothermal bulk modulus, coefficient of thermal expansion, heat capacity at constant volume and pressure, Debye temperature and Grüneisen parameter are computed for B1, B2 and B3 phases of AlSi alloy using quasi harmonic Debye model. Conclusions based on the structural, electronic and thermophysical properties of B1, B2 and B3 phases of AlSi alloy are summarized.